1922] Blum: On the Effect of Low Salinity on Teredo Navalis 359 



Factors limiting protection. — We may expect that if the water 

 within the burrow were diluted to a point much below the lethal 

 salinity (5 parts per 1000) the teredos would be killed, since the 

 animals die in a short time when directly exposed to water of less 

 salinity. Such a process of dilution is indicated by the following 

 experiment. 



TABLE 3 

 Survival or Teredo navalis in Standing Water* of Low Salinity in Aquaria 



* Water renewed every two days by passing stream of same salinity through 

 aquaria for a few moments. 



t Specimens acclimatized in 15 parts per 1000, and changed directly to lower 

 salinities. 



A specimen block containing teredos was removed from water 

 of 15 parts per 1000 salinity and placed above water in a closed 

 aquarium functioning as a moist chamber. In this way, evaporation 

 of the water in the wood was restricted, but no dilution of the water 

 in the burrows was possible. At the end of twenty-two days, the 

 specimen block was placed in salt water and approximately 50 per 

 cent of the original number of teredos extended their siphons. This 

 was a greater survival than that in water of and 2 parts per 1000 

 salinity for the same period of time. Table 4 shows the survival 

 periods under different experimental conditions. 



